Welded pressure vessel



Y Feb. l3, 1942. l. L. LANGVAND ETA; f 2,271,652

wELDED PRESSURE VESSEL Filed 11u1-y 1, 1959 s Sheets-sheet 1 7 2 V/lff//u imlfxarnljons [Var lag/grand BY @i l Wi ATTORNEY.

L l.. LANGVAND E-l-Al.I ?271',652l

WELDED PRESSURE' VESSEL. A

Filed July 1', 1939 5 Sheets-SlrxeetI 2 Fig noaaoaenonoaoaanaaoooev oaoonnnnncneoanaoaocn- 4 v INVENTORS 'f1/ar Llangvand BYA h Cec'i/H Gay y ATTORNEY.

5.5heets-Sheet 5 INVENTORS a# K ATTORNEY.

Feb. 3, 1942. l. L. LANGVAND ET AL WELDED PRESSURE VESSEL Filed July 1, 1939 [var Zang/rand QW Cecil lBY Patented Feb. 3, 1942 2,271,652 WELDED PRESSURE vEssEL` Ivar L. Langvand, Barberton, and Cecil H. Gay,

Akron, Ohio, assignors to The Babcock & Wilcox Company, Newark, N. J., a corporation of .New Jersey Application July 1, 1939, serial No. 282,466

6 Claims.

The invention relates to pressure vessels and more particularly to the heated class of pressure vessels of which steam boiler drums typify a commercially important group. These drums are constructed to operate at 'high pressure and with water and vapor at high temperatures as well. They must be so constructed that the necessary Water and steam connections can be suitably made; in addition, they must be so constructed that they can be readily inspected and that such internal apparatus as is found desirable for high pressure steam generators can be readily inserted or replaced.

The advent of vapor pressures-of over 1000 1b. per sq. in., together with temperature conditions encountered in present day steam generator practice, and in other industries such asA oil treatment and distillation processes for other products, has out-moded certain practices in the construction and manufacture of pressure vessels due to the fact that the behavior of the metal in walls of great thickness required to withstand heavy pressures and subjected to severe temperature difference between outer and inner wall surfaces is of a, character diiferent from thatwhere relatively low pressures and thin walls are used.

In the manufacture of relatively thin wall pressure vessels of -metal of comparatively low tensile strength and of considerable ductility, and where the temperature difference between outer and inner wall surfaces is small, it has been the practice to permit of certain self-adjustments the vessel walls to take care of localized bending effects and stress conditions resulting from causes', such as eccentricity, out of roundness in cylindrical vessels, non-uniform radial dilation over the head and shell, and temperature effects; and such self-adjustments have taken placeunder predetermined working pressures and temperatures to relieve localized high stress conditions Without serious consequences by reason of Aing local stresses must be eliminated. This is one object of the present invention.

With higher pressures of the order of 1400 lb.

per sq. in. and upward, the ratio of the specic vapor and liquid. (Ratio at 600 lb. per sq. ln.=37; at 1400 lb. per sq. in.=13; at 2000 lb. per sq.

Large diameter downcomer conduits which are used to effect circulation improvement under such conditions cannot be effectively connected to the drum by a' multiplicity of small expanded tubular conduits or by riveted anged nozzles which are Iadequate with lower pressure units, for

the connections must be such as to avoid appreciable uid ow resistance, yet be of adequate structural strength to carry the loads imposed under varying temperature and pressure conditions. H

It is an object of this invention to provide a boiler drum-of the high pressure type providing the fact that relatively low pressures and temity and mobility practically disappear; consei quently, with pressures of 1000 1b. per sq. in. or more, 'and temperature differences of large magnitude between outer and inner wall surfaces due to greater wall thickness, self-adjustments may no longer be depended upon, and factors increaslarge diameter'liquid connectors and access openings, in a manner which is adequate to meet the operating conditions and at the same time at a lower vcost than in the prior constructions.

Another object of the invention isV to provide a welded pressure vessel which has adequate ligament strength'between openings formed in the vessel for a tubular connection or foraccess openings, without adding or leaving excess metal elsewhere.

Another object of the invention is to provide a pressure vessel of non-uniform wall thickness with no excess metal above the strength requirement when tubular connections are joined to the vessel at certain zones.

A further objective is to provide a cylindrical pressure vessel of the heavy wall, high pressure type with hemispherical heads, and in which the required openings are located in a special zone in a manner which introduces no appreciable stress raisers as respectsv the body and head, the heads being of thinner metal than the body or any portion of it.

' Additionally, it may be stated that the invention provides a pressure vessel in which openings for external connections 'and for access are provided in such a manner that undesirable stress conditions are avoided.

In` pressure vessels for uid under high pressure there must be provided connections for fluid movement and for access to the vessels. Pressure vessels used for industrial fluid processes usually have cy1indrica1 bodies with heads of' some suitable form and when diameters are large or pressure high, or both, their walls must be quite thick, perhaps several inches, to keep metal stresses Within safe limits. openings as must be provided are for the admission or discharge of iiuid, for safety valves, and for other accessories, and in some cases openings are also provided for periodic inspection.

Fig. 8 is a side elevation of a drum with which downtake elements are associated in a modified manner; and

Fig. 9 is a detail view indicatingin section the manner of securing the downtake connections of the Fig. 8 drum. I

The pressure vessel indicated in Fig. 1 has two I components, namely, the body III and the hemi- Such connections or For numerous purposes to which pressure vesto cylindrical shape and with edges fusion weldedl together. constructing fusion welded pressure vessels with This invention provides a method of high safety factors in spite of the fact that they are provided with radial connections of large diameter.

The invention provides a pressure vessel having a short cylindrical section of the same internal diameter as the main cylindrical body of the pressure vessel but of larger external diameter and of greater wall thickness, and having the openings in the short and thick section for the large openings necessary for said connections. The length and thickness of the short cylindrical section is such as to keep the necessary metal stresses low enough for safety. 'The ends of this section are reduced in thickness to the same thickness as that of the cylindrical section to which it is fusion Welded, or to the head, thus insuring equal diametrical expansion under internal pressure of the metal on both sides of the circumferential weld. Toavoid local concentration of stresses in the thicker section due to its lesser thickness at its end than in its body, the change of thickness is made gradual.

' An additional feature of the invention resides in the manner and method by which connections are made to the thick cylindrical section.

With the above and other objects in view the invention will now be described in detail in connection with the accompanying drawings illustrating the same.

In the drawings: Y

Fig. 1 is `a longitudinal vertical section of'a portion of a Vpressure vessel constructed inaccordance with the present invention; Fig. 2 is a .sectional view on the line 2-2 of Fig. 1 looking in the direction of the arrows;

Fig. 3 is a view similar to Fig. 1 of a modified form of pressure vessel;

Fig. 4 is a sectional view on the line 4-4 of Fig. 3, looking in the direction of the arrows;

Fig. 5 is a fragmentary sectional view on the line 5-5 of Fig. 1, showing the particular construction by which the manhole cover is arranged relative to the drum; l

Fig. 6 is a verticalsection of a steam generating installation in which the illustrative pressure vessel is employed;

Fig. 7 is a vertical section on the line 'I-T of Fig. 6;

spherical head I2 welded thereto. 'I'he body I0 maybe a forging or the like integral with which is a `port sectionk I4 having a' Wall thickness greater than the remainder of the body I0, or the head I2. This accommodates large openings or ports I6 and I8, the increase in Wall thickness `compensating for the weakening due to the size of the openings.

The end of the -port section I4 is graduated? in thickness down to the thickness of the hemispherical drum head I2 so that goo'd welding conditions are provided. The drumhead I2 has its center in the longitudinal axis of the drum-'and is hemispherical in outline. This head is united with the port section I4 by a suitable girth weld 20.

One of the openings I6 or I8 may be counterbored as shown at 22 to receive the reduced end 24 of a tubular downcomer connector or the like 26. 'Ihe connectoris strength vwelded as at 30 A to the port section I4 while a seal weld 32 unites the thinner end 24 with the port section I4 on the drum interior. A large diameter downcomer 21 may be telescoped over the lower end of the connector 26 and welded thereto as indicated at 29.

It is to be noted that while the body I0 of the drum, the port section I4, and the hemispherical head I2 are of diii'erent wall thicknesses, nevertheless all are concentric so that there is a minimum of out-of-roundness to set up stresses and, furthermore, the body I0 and port section I4 are of the same internal diameter.

In Figs. 3 and 4 the construction is like that disclosed and described in reference to Fig. 1 except that the port section 36 is separate and at one end has a reduced section 38 of the same thickness as the body 40 for welding as at 42. The other end of the port section 36 is tapered as at 44 for effective union with the spherical head 46 by the weld 48.

The port or opening I6 indicated in Figs. 1, 2, and 3 may be of suflicient size to admit a workman to the interior of the drum and it may be closed by a anged plug or manhole cover 54 having its flange arranged within the drum and fitting a seat 50 formed in a vmanhole cover seat ring 52 welded to the drum, as shown.

The cover 54 for the access opening. I6 is shown in Fig. 5 to be in its drum closing position. It is held in this position by mechanical means involving the stud bolts 60. 'I'hese bolts are preferably rigid with the cover and they extend through yokes 62/y and 64 which are disposed across the opening. Nuts 66 and 66 are screwthreaded upon the bolts and tightened against the yokes 62 and 64 to maintain the cover in its operative position.

The cover 54 is also so arranged with reference to its seat in the ring 62 that the pressure of y in the ring 52.

Figs. 6 and 7 of the drawings illustrate the high pressure water tube steam generator in which the illustrative drum construction is employed. This installation operates at steam pressures of the order of 2200 lb. per sq. in., the major part ofthe steam being generated in the wall tubes 80-'84 defining the boundaries of the furnace 86. Burning fuel is projected downwardly into this furnace by the action of the burners 88-90 and the furnace gases flow from the furnace as indicated by the arrow 92 to a convection section 94 which includes the superheater 96 and the economizer 98.

The drum of the illustrative steam generator yis constructed at each end in the manner previously described, the thicker annular sections |02 and |04 near the ends of the drum having the large diameter downcomers |06 and |08 connected thereto. These downcomers are shown as communicating at their lower ends with the header I| 0 which may supply uid for the` furnace wall steam generating tubes 8|-84.

The drum 00 is supported by straps |20 and |22larranged adjacent the thicker drum sections |02 and |04 and secured at their upper ,ends to the beams |24` and |26.

By reason of the securement of many of the steam generating tubes of the unit directly to the drum |00 the drum, between its supports |24 and |26, acts as a support for a considerable part of the entire unit. However, the arrangement of the hangers or drum straps |20 `and |22 between the central part of' the drum and the downcomers |06 and |08 affords an arrangement of elements wherein the load comprising the weight ofthe drum and the parts secured thereto is advantageously distributed.

The illustrative method of pressure vessel construction involving the addition of an annular section at the end of the drum where the manhole openings and other large connections are made affords an advantageous means for supplying the annular section required for such open` f ings andresults in improved stress conditions in the entire shell of the vessel. Furthermore, it affords manhole connections or othertubular connections in which there is a possibility of X-raying the weld. This method of providing downcomer connections also eliminates a great number of smaller tubes which would otherwise be revquired and this, in turn, greatly reduces the length of the drum and eifects a consequent sav, ing in material.

In heavy drums for high pressures, it is practically impossible to fabricate drum heads having manholes of adequate thickness to safety withstand the pressures. This invention meets this situation by affording a method of drum manufacture in which the manhole can be placed verse bending stresses throughout the head and the shell adjacent the head. This is a highly advantageous feature in the manufacture of thick drum shells, because localized bending eiects'become very dangerous in thick plate constructions due to the great reduction in the ductility over the section of such plates. The illustrative construction reduces to a minimum the localized bending eects due to eccentricity and non-uniform radial dilations over the head and shell. Furthermore, the elimination of manhole openings from the drum head andthe use of unpierced hemispherical heads results in the very reasonable head thickness and thickness' of girth weld to the shell for the highest pressure, thus vgreatly facilitating the fabrication of such vessels.

The drum |30 shown in Fig. 8 of the drawings may be constructed in accordance'with the above described methods, but the downtake elements |32 and |34 are so associated with the re-enforced drum sections |36 and |38 that the entire load is transmitted directly to those sections. This takes place by reason of the seating of the shoulders |40 in correspondingly `formed recesses |42.in the drum wall. This method of attaching the downcomer connections eliminates the necessity of relying entirely upon weld metal for the safety of the structures. The shoulders on the downcomer elements |32 and |34 take the full pressure load without any assistance from the welds |44 and |46. In this modification these welds are primarily seal welds, their main function being to maintain pressure-tight joints between the downcomer connections and the d'um.

What is claimed is:

1. In a drum adapted to withstand high fluid pressures, a main body portion provided with a plurality of small diameter tube seats for lateral tube connections, a dished end section adaptedvto close the end of the drum, and an intermediate annular section of a wall thickness greater than that of the main body portion and also greater than the wall thickness of the end section, `said intermediate section being provided with a large diameter access opening, said end section being united with one end of the intermediate section and in axial alignment therewith by a girth weld, said main body portion being also circumferensection and in axial alignment therewith.

2. A welded pressure vessel comprising, a main body portion of one wall thickness, an annular in some other part of the drum. The hemispherical drum head construction involved in the illustrative drum permits the manufacturer to use drum head plate which is much thinner than that which would otherwise be required. Such a drum head is subject to comparatively accurate analysis and the relative thickness of the port section of the drum and the hemispherical drum head can be accurately set to-eliminate all tran ferential weld, the ends of the structure formed by the two bodies being normal to the longitudinal axis of the structure, the second body being of greater external diameter and greaterwall thickness than the first body and being provided withA a lateral opening with its axis passing through and normal to the axis of the entire structure, and an imperforate hollow head of substantially hemispherical outline welded to the second annular section to close an end of the` vessel.

4. In a cylindrical pressure vessel, a hollow cylindrical body having an annular section formed with large diameter access and circulationopenings, said annular section being of a wall thickness greater than the remainder of said body to compensate for the weakening effect of said openings, and end sections of substantially hemispherical contour .welded to said body to close the ends of the vessel.

5. In a drum adapted to withstand high iluid pressures, having a main body portion provided with a plurality of small diameter tube seats for lateral tube connections, a dished end section adapted to close the end of the drum, an intermediate annular section at least a part of which is of a wall thickness greater than that of the main body portion and also greater than the wall thickness of the end section, said intermediate section being provided with a large diameter opening, and a large diameter tubular element tting within said opening to extend outwardly of the drum and having a circumferential flange seated outwardly against the drum metal marginal to said opening, said rst mentioned section being united with one end of the intermediate section and in axial alignment therewith by a girth Weld, said main body portion being also circumferentially welded to the other end of the intermediate section and in axial alignment therewith.

6. In a pressure vessel or drum adapted to withstand high fluid pressures, a main body portion provided with a plurality of small diameter tube seats for lateral tube connections, a dished end section adapted to close the end of the drum, an intermediate annular section at least a part of which is of a wall thickness greater than that oi the main body portion and also greater than the wall thickness of the end section, said intermediatesection being provided with a large diameter opening, the thicker metal of said intermediate annular ysection marginal to said opening being formed to provide a circumferential shoulder facing inwardly of the drum, and a tubular member extending laterally of the drum and having a circumferential flange seated against said shoulder and welded to the adjacent drum metal, said nrst mentioned section being united with one end of the intermediate section and in axial alignment therewith by a girth weld, said main body portion being .also circumferentially welded to the other end of the intermediate section and in axial alignment therewith.

IVAR L. LANGVAND. CECIL H. GAY. 

